Greaseproof paper



Patented Jan. 19, 19 43 GBEASEPROOF PAPER Richard D. Freeman, Floyd 0.Peterson and George K. Greminger, Jr., Midland, Mich, assignora to TheDow Chemical Company, Midland, Mich., a corporation of Michigan NoDrawing. Application March 0, 1941, Serial No. 382,104

l 2 Claims. (Cl. 117-157) This invention relates to an improved methodof preventing greasy and oily exudations from paper packages of productswhich tend to give such exudates through paper.

It is well known that many articles of commerce of an oily or greasynature are ordinarily packaged in special containers which addmaterially to the cost of the product, but which are made necessarybecause of the tendency of such products to exude oil or grease throughpaper or other commercially available packaging or wrapping material.Thus it is the practice to package, for example, peanut butter,lubricating oil, salad oil, shortening, and many other products, inglass or metal containers. Similarly, butter, bacon, soap, and manypharmaceutical products of a particularly oily or greasy nature arecustomarily wrapped in specially treated paper such as parchment and thelike, or are enclosed in multi-layers of wrapping material in an attemptto minimize emission of oil or grease through the container. Most of thecommercially available wrapping papers are but partially successful inaccomplishing the desired end. It may easily be recognized that it wouldbe highly desirable to be able to package greasy or oily products of alltypes in paper containers rather than in the more expensive packagingmaterials now employed.

It is, accordingly, an object of the invention to provide a methodwhereby greasy and oily products, or products tending to give greasy oroily exudations through paper, may be enclosed in paper containerswithout danger of giving such exudates therethrough.

It has now been found that the foregoing object may be accomplished byenclosing the above suggested type of greasy and oily products in papercontainers bearing a substantially continuous surface coating comprisingas the essential ingredient a polyvalent metal salt of celluloseglycollic acid. The packaging material employed may be prepared bycoating wrapping paper, cardboard, Bristol board, or box board, with anaqueous alkaline solution of a polyvalent metal salt of celluloseglycollic acid, to be defined more particularly hereinafter. Any of theconventional coating methods may be used for applying and spreading thecoating which is normally deposited in such thickness as to insure theenclosure within the coating of any upstanding fibers on the papersurface.

The salt of cellulose glycolllc acid used in the present invention ispreferably one which is derived from that type of cellulose glycollicacid whose alkali metal salts are soluble in water. Such celluloseglycollic acid usually contains from about 0.4 to about 0.8 etheriiyinggroups per anhydro-glucose unit. The polyvalent metal salts of this typeof cellulose glycollic acid are substantially insoluble in organicsolvents and are unaffected by oils and greases of all types, includingmineral, vegetable, and animal oils, natural fats, synthetic shortening,and waxes, both of the hydrocarbon and the ester type. The polyvalentmetal salts which may be employed include those of aluminum, zinc,titanium, tin, iron, chromium, copper, nickel, cobalt, zirconium, andthe like, though, because of the requirement that coating materials foruse in connection with foodstufis be non-toxic, it is preferred toemploy aluminum cellulose glycollate, particularly in those packageswhich are to be employed in conjunction with foodstuffs. Aluminumcellulose glycollate is a colorless, odorless, and non-toxic product,insoluble in water but soluble in dilute aqueous solutions of alkalies.All of the polyvalent metal salts of cellulose glycollic acid suggestedabove may be brought into solution in an aqueous medium by incorporatingin said medium from 0.2 to 1 per cent of an alkali which preferablyshould be of the volatile type, c. g., ammonia. Coatings deposited onpaper from such dilute solutions of the polyvalent metal celluloseglycollates are not only impermeable to greases and oils, but remainunbroken in the presence or water, except when the amount of waterpresent is sumcient to disintegrate the paper base.

when the coating comprising a polyvalent metal cellulose glycollate isapplied to a very smooth surfaced paper base under optimum coatingconditions, a continuous film of the salt may be only of the order of0.1 mil thick. When, however, a rough surfaced paper is to be employedit may be necessary to apply a coating of the order of 2 mils or more inthickness in order that it be continuous. All these coatings, includingthe thick ones, are tough and flexible and remain unbroken aftercreasing and handling, and consequently retain their impermeability togrease and oil after such treatment.

The following example illustrates the manner in which the preferredpackaging materials may be produced and the advantages accruing to thepresent invention. A solution was prepared by dissolving 4 parts byweight of water-insoluble aluminum cellulose glycollate in parts byweight of 0.5 per cent ammonium hydroxide. The solution wasspread on asheet of paper board with the aid of a doctor knife, at a thicknesssufllcient to cover the upstanding suriace vfibers oi the board. Thecoating was dried and the paper board cut into sections for testpurposes to determine the degree of grease prooiness aiiorded by thesurface coating. Various oils and greases were pressed upon both flatand folded pieces oi the coated paper. The i'olded pieces employed as atest of the eflect oi creasing upon grease resistance weremade fromsquares of the paper 2.5 inches on a side. folded to form boxes 10 1.5inches square at the base and with sides 0.5 inch high. The boxesemployed in the crease test were held in shape by suitable supports.Each of the samples being tested was examined periodically for signs ofpenetration of oil or 15 grease. Uncoated specimens failed in less than1 hour in the case of oils such as peanut oil and in less than 24 hoursin the case of tats such as butter. The coated specimens both flat andcreased were still satisfactory after 120 hours in contact with oil orfats. The foregoing test was conducted at room temperature but similartests carried out at 70 0. indicated that the coated wrapping materialsof the present invention withstand the effects of oil and grease at thiselevated 5 temperature for periods up to 200 hours or more withoutfailure; depending in part upon the thickness of the deposited coating.

Because of the combination of advantageous properties, includingresistance both to water and to oily substances, the present inventionoflers considerable advantage over the use or papers coated with othercellulose ethers heretofore disclosed as having certain grease proofingcharacteristics.

We claim:

1. The method for grease-proofing a paper sheet which includes: treatingat least one surface oi the sheet with an aqueous solution of aluminumcellulose glycollate and ammonia; and

drying the treated sheet.

2. The method which includes: dissolving aluminum cellulose glycollatein dilute aqueous ammonia; coating a paper sheet with the so pre- 20pared solution; and drying the coated sheet.

RICHARD D. FREEMAN. FLOYD C. PETERSON. GEORGE K. GREMINGER. JR.

